The ultimate goal of the proposed research is to understand the regulation of stable RNA in genes in E. coli. This knowledge is in turn central to understanding the regulation of bacterial growth. To achieve this large goal, it is necessary that a variety of stable RNA gene systems be examined and the relevant regulatory mechanism for each described. The PI hopes to contribute toward this knowledge by studying the argT operon. The proposed studies are based on the use of a argT promoter-galactokinase gene fusion plasmid, pMR1y1, to provide a direct and simple assay of the promoter activity in vivo. By measuring the gene copy specific Ga1K level at different growth rates, the argT promoter was shown to undergo growth rate dependent regulation. Deletion mutagenesis further revealed the requirement of an upstream activation sequence and the existence of a downstream terminator. Stringent control studies, performed by a hybrid- protection method, suggested the argT promote to escape stringency. In addition, in vitro transcription from the argT promoter was found to be repressible by LexA protein. Thus, a rather unique set of regulatory response seem to govern the activity of this tRNA gene promoter. Further studies described herein propose to pinpoint the genetic signal(s) responsible for each control by in vitro mutagenesis and DNase I footprinting analysis. The biochemical mechanism involved will be elucidated by determinations of binding constants and identification of effector molecules.